The pty master read() can miss the wake up for a packet mode
status change. For example,
CPU 0 | CPU 1
n_tty_read() | n_tty_packet_mode_flush()
... | .
if (packet & link->ctrl_status) { | .
/* no new ctrl_status ATM */ | .
| spin_lock
| ctrl_status |= TIOCPKT_FLUSHREAD
| spin_unlock
| wake_up(link->read_wait)
} |
set_current_state(TASK_INTERRUPTIBLE) |
... |
The pty master read() will now sleep (assuming there is no input) having
missed the read_wait wakeup.
Set the task state before the condition test.
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
drivers/tty/n_tty.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 6a42204..602dbc2 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2168,6 +2168,11 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
add_wait_queue(&tty->read_wait, &wait);
while (nr) {
+ /* This statement must be first before checking for input
+ so that any interrupt will set the state back to
+ TASK_RUNNING. */
+ set_current_state(TASK_INTERRUPTIBLE);
+
/* First test for status change. */
if (packet && tty->link->ctrl_status) {
unsigned char cs;
@@ -2185,10 +2190,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
nr--;
break;
}
- /* This statement must be first before checking for input
- so that any interrupt will set the state back to
- TASK_RUNNING. */
- set_current_state(TASK_INTERRUPTIBLE);
if (((minimum - (b - buf)) < ldata->minimum_to_wake) &&
((minimum - (b - buf)) >= 1))
--
2.1.1
--
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